The landing phase is very short compared to the duration of a flight, it constitutes the transition between the flight and taxiing on the ground. However, accidents occur for many reasons: approach speed too high for the runway length, poor assessment of the runway conditions, runway touchdown point too distant, etc. Examples can be cited, taken from publications of enquiry reports produced by the Bureau d'Enquêtes et d'Analyses for safety in civil aviation. The objective of the following examples is to define the issues in the field.
Accident involving a 747 operated by the French airline Air France that occurred on 13 Nov. 1993 at Tahiti Faaa airport. In the final approach phase, the active pilot sought to counter an automatic go-around triggered by the automatic flight system. He continued the approach by over-riding the automatic throttle. During the landing, the left outer jet engine started up in positive full thrust mode. The aircraft then left the runway to the right and finished up in the lagoon. The accident was due to an unstabilized approach and the selection of strong positive thrust mode for engine 1 on landing, consequence of a peculiarity of the automatic flight system leading to the transition to go-around mode at a point in the trajectory corresponding to the decision height. This led to the long touchdown with excessive speed and the deviation from the trajectory to the right and the lateral exit from the runway.
Accident involving a 747 operated by Cameroon Airlines that occurred on Nov. 5, 2000 at Paris Charles de Gaule airport. The aeroplane diverted from the runway axis and left the runway, tearing the landing gear and damaging the airframe. The probable cause was the incomplete reduction of the left outer engine at the start of deceleration, having led to the deactivation of the automatic braking systems and the non-release of thrust reverser No. 1. The inadvertent setting of this engine to full power after landing generated a strong thrust dissymmetry that caused the aircraft to leave the runway.
Accident involving an A340 operated by Air France that occurred on 2 Aug. 2005 at Toronto airport. The plane made a long landing on the landing runway and left the end of the runway to finish up in a ravine just outside the perimeter of the airport and the aircraft was destroyed by fire. The probable cause originates from the fact that, during the levelling-off sub-phase of the landing phase, the aircraft entered into an area of strong showers, the wind had turned leading to a tailwind component of approximately 5 knots. The runway had become contaminated, being covered with at least a quarter inch of stagnant water. The aircraft touched the ground at a distance of approximately 4000 feet on the 9000-foot runway.
Nowadays, the systems used are systems that enable the pilot to choose the type of braking: strong, moderate, weak according to the landing runway length and the runway exit chosen to begin the route to the airport area.
There are patent documents that describe a device displaying the stopping position of the aeroplane and supplying the appropriate deceleration commands to the braking system for the aeroplane to be able to leave the chosen taxiway. Not all aircraft can be equipped therewith, because such devices involve complex devices with a plurality of miscellaneous collaborating computers. Among these documents, there is U.S. Pat. No. 5,968,106 describing an automatic braking system that makes it possible to finalize the travel of an aircraft at a precise point.
The systems described hereinbelow take into account the current deceleration conditions to predict and calculate the braking distance. This basic calculation mode does not always make it possible to offer a relevant alert.
One known system is described in French patent application FR 2842337. This is a method and device to assist in the driving of a vehicle that makes it possible to calculate and display the distance needed to reach a particular speed value according to an initial speed and a defined deceleration. This system makes it possible, for example, to assess the distance needed to perform a landing. However, the assessment method does not take into account the external braking conditions, notably the meteorological parameters.
Also known is for French patent application FR 2897593 describing a method and a system predicting the possibility of completely stopping an aircraft on a landing runway. This application takes account only of the descent angle of the approach to calculate the deviation relative to the runway threshold.
The solutions described in these documents do not make it possible to implement a solution for monitoring the landing phase. The solutions described do not take into account the meteorological conditions, the status of the landing runway, the parameters and the flight configurations of the aircraft, notably the engine specs and aerofoil configuration. The examples of accidents cited above show that they are due to the weather, inappropriate flight manoeuvres or automatic flight control instructions that are inconsistent with the landing phase.